Posted by: tom.guerry (tom.guerry@kp.org) on Wed Feb 28 14:48:30 2007

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> Hi Tom
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> For me to understand your post, I need to know what “Internal” and “external” rotation of the lead-arm means. Example : Does “external” rotation of the arm causes the wrist to roll? Why would “internal” rotation not cause the wrist to roll? What forces does “internal” rotation of the lead-arm apply to the bat when the lead-shoulder is stationary?

Good question, it can be hard to sort out internal/external rotation of the humerus in the shoulder socket (usually called "shoulder" internal/external rotation even though it is the humerus/arm bone that is rotating) from forearm twist/supination/pronation, particularly if the arm is pretty straight as it is in golf.

When the arm is bent, however, there is quite a noticeable difference.

In ANY case, the BEST way to look for internal/external rotation is by seeing how the elbow is pointing. The knob on the elbow is anatomically called the "olecranon process" and is actually part of the major forearm bone, the ULNA. However, when the forearm twists, this part of the ulna does NOT. This allows you to make the distinction between how much twist of your hand/palm might be due to internal/external rotation of the upperr arm bone humerus vs how much is due to twisting of forearms (pronation/supination).

For example. if you have your arms hanging down at your side with the arms pretty much straight, we can focus on the lead arm.

Looking down at your left hand, you can rotate the hand clockwise as far as it can go by twisting both the upper arm in the shoulder socket (internal rotation) and by twisting the forearm ,"pronating it" as much as possible.

When you do this you can twist the hand enough so that the palm is facing forward toward the pitcher if you were staning in the batters box.

Now you can rotate the hand counterclockwise as much as possible. A golf pro might call this "supination" , twisting the forearm to turn the hand away from the body, BUT the movement can result from a combination of upper arm/humerus twist (external rotation) as well as forearm twist in the supinating/counter-clockwise direction.

You can tell how muc external rotation is involved by seeing how much the point of the elbow/olecranon process moves.
It has a range of motion of perhaps a little more than 90 degrees.

The remainder of the twisting motion is from forearm supination, perhaps an additional 180 degrees.

So arm internal/extetrnal rotation will differ in how it affects the wrists depending on if the arms are bent at the elbow or not.

If the elbow is bent at 90 degrees, then you will just move the forearm without twisting/rolling the wrists.

Usually when the lead arm internally rotates in the hitter just after the back arm and lead leg start externally rotating togteher, the internal rotation of the lead arm causes the wrist to move in what appears to be a "pronating" direction so that a vertical bat would start dropping toward the developing swing plane.
When done well and in sequence, this is part of both avoiding wrist bind AND not overshooting/wobbling the swing plane.

You can likewise "PRONATE" the lead wrist through contact WITHOUT disconnecting/while KEEPING the lead arm internally rotated to give the appearance of wrist roll through contact but with NO wrist bind or disconenction. This would be shown By Hank Aaron, for example due to his choke grip and qhort swing radius.

He moves his scaps and twists the forearms and rolls the wrists but withouit disconnecting or wobbling the swing plane due to the lead arm staying internally rotated in the socket/"keeping the elbow pointint (olecranon process) in the swing plane".
>
> Jack Mankin